Mongoose populate an array field with another Model object

Question

I am really confused on how to approach this problem. I want to populate my studyGroups array of my User model with a specific StudyGroup model. I obtain the specific user and studyGroup through the router (cuid: req.params.cuid for the users, and guid: req.params.guid for the studyGroup).

Here is what my code looks like:

User

const userSchema = new Schema({
  cuid: { type: 'String', required: true },
  firstName: { type: 'String', required: true },
  lastName: { type: 'String', required: true },
  studentId: { type: 'Number', required: true },
  password: { type: 'String', required: true },
  email: { type: 'String', required: true },
  dateAdded: { type: 'Date', default: Date.now, required: true },
  lastLogin: { type: 'Date', default: null, required: false },
  studyGroups: [
      {
        type: mongoose.Schema.Types.ObjectId,
        ref: "studyGroup"
      }
    ]
});

StudyGroup

const studyGroupSchema = new Schema({
  guid: { type: 'String', required: true },
  groupName: { type: 'String', required: true },
  course: { type: 'String', required: true },
  teacher: { type: 'String', required: true },
  description: { type: 'String', required: true },
  dateAdded: { type: 'Date', default: Date.now, required: true },
});

Route

router.route('/:cuid/studyGroups/:guid').post(UserController.addUserStudyGroups);

Here is where all the action happens. First I find the user, and now I want to add the whole studyGroup model object to the array. So my thought was to query the studyGroup using the guid: req.params.guid but don't know if that is the proper way.

Controller

export function addUserStudyGroups(req, res) {
  User.findOne({ cuid: req.params.cuid }).populate('studyGroups').exec((err, studyGroups) => {
    if (err) {
      return res.status(500).send(err);
    }
    study
    return res.json({ studyGroups });
  });
}

sidgate · Accepted Answer · 2017-02-21 02:26:38Z

1

You can now do it in Mongo 3.2 using $lookup

$lookup takes four arguments

from: Specifies the collection in the same database to perform the join with. The from collection cannot be sharded.

localField: Specifies the field from the documents input to the $lookup stage. $lookup performs an equality match on the localField to the foreignField from the documents of the from collection.

foreignField: Specifies the field from the documents in the from collection.

as: Specifies the name of the new array field to add to the input documents. The new array field contains the matching documents from the from collection.

db.User.aggregate(
  {$unwind: "$bars"},
  {$lookup: {
    from:"studyGroups",
    localField: "studyGroups",
    foreignField: "_id",
    as: "studyGroupList"

   }}
)

answered Feb 21, 2017 at 2:26

sidgate

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